Modular prestressed concrete marine vessels and method of making same

ABSTRACT

A preferred method of fabricating a prestressed concrete barge is disclosed in which the hull is constructed from a plurality of longitudinal modules. All modules, including the bulkhead modules, are cast in a horizontal plane as a full-transverse cross-sectional element with appropriate spaced openings. Then the modules, which have ducts extending therethrough and a gasket sealing one end of each duct, are rotated 90* to a normal, or vertical, orientation, post-tensioned in two complementary directions, and transported to an assembly site. Steel tendons are passed longitudinally through the ducts so that the modules can be lightly prestressed until the adjacent modules are in alignment. The joints defined by adjacent modules are then temporarily sealed by applying a putty-like cement or grout thereinto; an adhesive epoxy is subsequently pumped into the temporary joint to form a full-strength, long-lived, water-tight bond. The procedure is repeated until the hull has been completed, and then the entire hull is longitudinally prestressed by applying considerable force to the tendons. Grout is then pumped into the ducts and allowed to harden to maintain the tensioning forces of the tendons, which act in a third complementary direction. Storage tanks are then installed from the open ends of the assembled hull onto saddles located in the interior of the hull. Concrete plugs are then sealed in the openings of the bulk-head modules. The bow and stern, which are cast as separate, doublecurved, non-prestressed concrete sections, are then joined to the modular hull. Lastly, the barge is launched and a plurality of tanks are secured to saddles on the deck. The unique method outlined above, with minor variants, is applicable to the fabrication of concrete barges for transporting liquid petroleum gas (LPG), liquid natural gas (LNG), vinyl chloride and various cryogenic cargoes. Furthermore, such method may be utilized to fabricate diverse modular floating platforms well-suited for use as self-contained electrical power generating stations, waste treatment facilities, fish canneries, heliports, and the like.

nite 11 States Gerwick, Jr. et al.

3 atent [191 MODULAR PRESTRESSED CONCRETE MARINE VESSELS AND METHOD OF MAKING SAME [76] Inventors: Ben C. Gerwick, Jr., 500 Scansom St., San Francisco, Calif. 941 l 1; William J. Talbot, Jr., 3601 Sarsalite Dr., Corono Del Mar, Calif. 94965; Keith E. Hughes, 2570 Qued Way, Laguna Beach, Calif. 92651; Arnold L. Brown, Snowdon Ct., Walnut Creek, Calif. 92651 [22] Filed: Apr. 9, 1973 [21] Appl. No.: 349,405

Primary ExaminerTrygve M. Blix Attorney, Agent, or Firm-Eric P. Schellin; Martin P. Hoffman [57] ABSTRACT A preferred method of fabricating a prestressed concrete barge is disclosed in which the hull is constructed from a plurality of longitudinal modules. All modules, including the bulkhead modules, are cast in a horizontal plane as a full-transverse cross-sectional element with appropriate spaced openings. Then the modules, which have ducts extending therethrough and a gasket sealing one end of each duct, are rotated 90 to a normal, or vertical, orientation, posttensioned in two complementary directions, and transported to an assembly site. Steel tendons are passed longitudinally through the ducts so that the modules can be lightly prestressed until the adjacent modules are in alignment. The joints defined by adjacent modules are then temporarily sealed by applying a puttylike cement or grout thereinto; an adhesive epoxy is subsequently pumped into the temporary joint to form a full-strength, long-lived, water-tight bond. The procedure is repeated until the hull has been completed, and then the entire hull is longitudinally prestressed by applying considerable force to the tendons. Grout is then pumped into the ducts and allowed to harden to maintain the tensioning forces of the tendons, which act in a third complementary direction. Storage tanks are then installed from the open ends of the assembled hull onto saddles located in the interior of the hull. Concrete plugs are then sealed in the openings of the bulk-head modules. The bow and stem, which are cast as separate, doublecurved, non-prestressed concrete sections, are then joined to the modular hull. Lastly, the barge is launched and a plurality of tanks are secured to saddles on the deck.

The unique method outlined above, with minor variants, is applicable to the fabrication of concrete barges for transporting liquid petroleum gas (LPG), liquid natural gas (LNG), vinyl chloride and various cryogenic cargoes. Furthermore, such method may be utilized to fabricate diverse modular floating platforms well-suited for use as self-contained electrical power generating stations, waste treatment facilities, fish canneries, heliports, and the like.

17 Claims, 32 Drawing Figures PAIENIED M18 1 31974 SHEET 01 BF H PAIENTEB AUG 1 3 i9 74 SHEU 02 HF 11 PAIENIED m1 31914 I 3.828. 708

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SHEET 211 OF H MODULAR PRESTRESSED CONCRETE MARINE VESSELS AND METHOD OF MAKING SAME BACKGROUND OF THE INVENTION 1. Field of the Invention This invention pertains to prestressed concrete marine vessels of modular construction, and to unique techniques for fabricating such vessels.

2. Description of the Prior Art Due to the shortage of steel during World War I, interest was focused on reinforced concrete as a substitutc for steel, and a limited number of crude concrete vessels were built. After World War I, interest in concrete vessels waned, only to be reawakened by World War ll. The Navy then constructed several dozen reinforced concrete barges or lighters and two dozen reinforced concrete, self-propelled cargo vessels. By the end of World War II, the Navy had successfully evaluated a concrete landing craft, but the project was terminated with the cessation of hostilities and the ready availability of steel.

One of the first vessels to utilize prestressed concrete, as contrasted with the previously utilized reinforced concrete, is disclosed in US. Pat. No. 2,344,223 granted to Maxwell M. Upson and John N. Philbrook. This patent recognized that the dead weight of known steel reinforced concrete vessels restricted the capacity of such vessels, and that unstressed steel reinforcing members led to high construction costs. Consequently, Upson, et al, disclosed a prestressed reinforced concrete vessel including precast bow and stem sections, and a plurality of similar precast waist sections intermediate the bow and stem sections. A plurality of longitudinally extending steel reinforcing rods projected from opposite sides of the waist sections, and the waist sections were mounted on skids which were supported on a concrete bed extending between vertical concrete abutments. The ends of the rods were threaded so that a tubular yoke was slipped over the aligned ends of the rods of the adjacent waist section, and a nut was screwed onto the end of each rod. The slack in the rods was taken up by tightening the nuts with a wrench. Tension was then applied to the remote ends of the rods, which were embedded in the abutments, by hydraulic rams which moved one abutment relative to the other. Such tension was maintained on the system while concrete bulkheads were positioned at the joints, and then concrete was poured between the end surfaces of the adjacent section.

While in theory, at least, Upson, et al, represented a significant A advance over prior techniques, several shortcomings were noted. For example, difficulties in maintaining the joints between sections water-tight were a common and severe problem with concrete vessels. Also, problems were encountered in manipulating the cumbersome 25 foot cast waist sections, in properly aligning same with respect to one another, and in applying uniform tensioning forces to the longitudinally extending rods. Furthermore, the maximum ship size envisioned by the Upson, et al, patent was but 208 feet in length, with a 35 foot beam and a load-carrying capacity far too limited to be operated at profitable level.

In more recent years, due to the significant advances in prestressed concrete technology and the continuing quest for an inexpensive, efficient vessel to transport liquid natural gas and/or liquid petroleum gas from remote fields to central processing facilities, numerous other atempts have been made to fabricate a commercially feasible concrete vessel. One of the more promising attempts is set forth in US. Pat. No. 3,324,814, granted to Alfred A. Yee.

Yee discloses a vessel with a prestressed unitary concrete hull section reinforced by a plurality of longitudinally spaced frame-like rib sections which are interconnected by virtue of a plurality of longitudinally extending structural members. Bulkheads are utilized in conjunction with the rib sections to form individual cargo holds within the hull. Longitudinally extending steel rods or tendons are spaced circumferentially about the girth of the hull and are placed under great tension by suitable anchor assemblies. Mild steel reinforcing rods are then passed about the transverse dimension of the vessel, to complete the framework for the hull. Then, cement is poured between the inner and outer surfaces of a mold that surrounds the framework while the tendons are maintained under tension. The extreme longitudinal portions of the tendons are also bent over to form a skeleton frame for the bow and stern sections, and cement is molded thereover in a similar manner. The bow, hull and stem are then bonded together to complete the vessel.

While Yees reliance upon a unitary hull circumvents the difficulties of aligning the plurality of precast sections utilized by Upson, et al, and effectively joining same together, the problems of molding and moving the immense central hull remains unsolved. Additionally, the hull is only prestressed in the longitudinal direction and reinforced in its lateral dimensions and must rely upon the internal framework for strengthening the vessel. Such framework is expensive to install and limits the commercial feasibility of the Yee approach.

Another attempt to design a vessel ideally suited for transporting liquid natural gas and/or liquid petroleum gas or other liquid gases at cryogenic temperatures is set forth in US Pat. No. 3,498,249, granted to Terrell M. Jones. Jones discloses a cargo vessel with conventional metallic bow and stern portion and a plurality of concrete cargo holds fastened therebetween. Each cargo hold includes a concrete inner wall, a concrete outer wall, and structural steel webs separating the walls from one another. A plurality of elongated prestressing tendons are passed through conduits in the concrete to exert a compressive force upon the concrete walls, and a lining of insulation with a liquid impervious membrane barrier is secured to the inner wall of each cargo hold.

The size of each cargo hold section makes such components difficult to manipulate, align, and seal together. Additionally, the double-wall construction with the structural steel web separators and the complex insulating technique lead to high fabrication costs and limit the commercial feasibility of such technique.

SUMMARY thickness, and prestresses such modules in three directions, for added strength and load carrying capacity. Each module, including the bulkhead module, is cast as a full-transverse cross-sectional element. The modules are bonded together along contiguous surfaces by applying grout, letting it harden to form a temporary joint or seal, and then pumping in epoxy to permanently join the modules together. The seal formed by such technique is long-lived and water-tight, and vessels as large as 675 feet in length and 80 feet to 100 feet across can be constructed.

All of the modules have a comparable frame-like outline so that they can be lifted and positioned with far greater ease than the massive sections utilized in prior concrete construction techniques. A minority of the modules must serve as bulkheads to lend structural rigidity to the hull and to anchor the longitudinally extending tendons. In practicing the instant technique, concrete plugs are cast to match the opening in the bulkhead modules. After the hull has been assembled and the storage tanks inserted thereinto, the plugs are jacked up into position to fill the openings in the bulkhead modules and are then adhesively sealed in place and prestressed to the frame. The similarity of the sections, despite the differences in function, insures that the modules will deform in a similar manner in response to various stresses applied thereto.

The marine vessels formed by the instant technique may assume various shapes and may perform sundry functions, although the preferred embodiment is a modular concrete prestressed barge several hundred feet in length with a huge cargo carrying capacity for transporting liquid petroleum gas. In alternative embodiments, the invention discloses a modular concrete prestressed barge for transporting liquid natural gas. The barges have conventional tanks located therein in such a manner that the concrete, which is not embrittled by the cryogenic cargo, can function as a secondary barrier in the event of an accidental rupture of a tank. Other embodiments envision modular floating platforms specially equipped to generate electrical power, to treat waste, to process fish, act as a heliport, and the like.

Other advantages of the instant fabrication technique, and the marine vessels constructed thereby, will become readily apparent from the following description of the invention when construed in conjunction with the accompanying sheets of drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a preferred embodiment of a barge constructed in accordance with the principles of the instant invention, with a fragment broken away for illustrative purposes;

FIG. 2 is an exploded perspective view of the barge of FIG. 1;

FIG. 3 is a perspective view of a longitudinal frame module after it has been cast in a horizontal plane;

FIG. 4 is a perspective view of the frame module after it has been turned 90 from the position of FIG. 3 and is being transported by a gantry;

FIG. 5 is a perspective view of a pair of frame modules being lightly prestressed into engagement;

FIG. 6 is a front elevational view of bulkhead module;

FIG. 7 is a side elevational view of the bulkhead mod ule, such view being taken along line 7-7 in FIG. 6 and in the direction indicated;

FIG. 8 is a side elevational view of the bulkhead module with a plug positioned for insertion into the module;

FIG. 9 is a side elevational view of the bulkhead module with a plug inserted thereinto;

FIG. 10 is an exploded perspective of the bulkhead module with one plug positioned for insertion into the module;

FIG. 11 is a perspective view of a hull that has been formed from a plurality of longitudinal frame and bulkhead modules;

FIG. 12 depicts a storage tank being inserted into the hull;

FIG. 13 shows the bow and stem section secured to the opposite ends of the hull;

FIG. l4A-l4B is a vertical cross-sectional view through the barge shown in FIG. 13, such view being taken long line l4l4 in FIG. 13 and in the direction indicated;

FIG. ISA-15B is a vertical cross-sectional view through the barge of FIG. 13, such view being taken along line 1515 in FIG. 13, and in the direction indicated;

FIG. 16 is a vertical cross-sectional view through the barge of FIG. 1, such view being taken along line 16-16 in FIG. 1, and in the direction indicated;

FIG. 17 is a vertical cross-sectional view, on an enlarged scale, of a segment of the hull depicting the manner in which adjacent modules are bonded together;

FIG. 18 is another vertical cross-sectional view of the fragment of the hull seen in FIG. 17, such view being taken along line l8l8 in FIG. 17 and in the direction indicated;

FIG. 19 is a horizontal cross-sectional view of a fragment through the bottom of the hull of the barge, such view being taken along line 1414 in FIG. 10 and in the direction indicated;

FIG. 20 is a horizontal cross-sectional view of a fragment of a bulkhead of the barge, such view being taken along line 2020 in FIG. 15 and in the direction indicated;

FIG. 21 is a top plan view of a first alternative embodiment of a barge constructed in accordance with the principles of the instant invention;

FIG. 22 is a side elevational view of the barge of FIG. 21;

FIG. 23 is a vertical cross-sectional view of the barge of FIGS. 21 and 22, such view being taken along line 2323 in FIG. 22 and in the direction indicated;

FIGS. 24-27 show four additional alternative embodiments of marine vessels constructed in accordance with the principles of the instant invention;

FIG. 28 shows a perspective view of a modification of the longitudinal frame module;

FIG. 29 shows a side elevational view of modules of FIG. 28 being joined together; and

FIG. 30 shows a perspective view of a modification of the bulkhead module.

DESCRIPTION OF THE INVENTION Referring now to the drawings wherein identical reference characters designated identical components, FIGS. 1 and 2 show a prestressed concrete barge identified generally by reference numeral 10. Barge 10 includes a bow 12, a hull l4, and a stern 16. A plurality of storage tanks 18 are secured to the deck of barge by saddles 20, and a like plurality of storage tanks 22 are secured in a similar manner within hull 14, which is hollow in construction. A fragment of hull 14 is broken away to reveal the underlying network of prestressing steel that imparts great strength and structural rigidity to barge 10.

The steps involved in the technique for fabricating hull 14 are shown in sequence in FIGS. 3-13. FIG. 3 shows one of the plurality of longitudinal frame concrete modules 24 that, in conjunction with a lesser number of bulkhead modules, comprise hull 14. Each module 24 is cast in a horizontal position in a conventional concrete form. The form (not shown) may be made of steel, or plywood backed by steel, and sufficiently rigid and accurate to give tolerances of onequarter of an inch at any given point. A reinforcing steel network (shown in the fragmentary broken away portions of FIGS. 1 and 3) is laced within the form prior to the concreting operations. A plurality of metal ducts 26, which extend through the module, are rigidly tied into the reinforcing steel network. The ducts are capped and sealed during the concreting operation to prevent entry of foreign materials into the ducts. After the concreting operation is completed, the module is cured.

More particularly, a second module 24 is cast in an overlapping relationship on top of a first module 24, so that the joint defined therebetween will match perfectly. After the second module has been cured, it is moved down to ground level, and the first module is moved to storage. Then a third module is cast in overlapping relationship atop the second module, and the casting procedure is repeated several times until the hull is completed. It will be noted that the transverse and vertical prestressing of each module takes place after it has been cured and placed in storage.

FIG. 4 shows module 24 after it has been turned 90 by a special rotating shoe from its horizontal orientation into a normal or vertical orientation and is being transported by a gantry to an assembly basin or a launchway. After rotation, the reinforcing steel network is post-tensioned, in one or two stages, in two vertical planes normal to one another. Such planes are indicated by directional arrows x and y in FIGS. 3 and 4. Ducts 26 extend through module 24 in the 2" or longitudinal direction when the module is in its normal, or vertical orientation. Each module may be 4 to 6 feet in longitudinal dimension, and its transverse dimension is equivalent to the full width of bull l4. Module 24 may be 96 feet across in the preferred embodiment of barge 10.

FIG. 5 shows a second module 24b after it has been positioned adjacent to a first module 24a by the gantry shown in FIG. 4. Ducts 26 are opened so that a plurality of steel tendons 28 can be passed longitudinally therethrough. Prior to inserting the tendons, ducts 26 are flushed with fresh water, then blown out with compressed air. By sliding the modules along tendons 28, each module is placed in proximity to the preceding module. Alternatively, the modules can be positioned in proximity to one another by exerting a slight, prestressing force. In either instance, the contiguous surfaces of the modules, such as modules 24a, 2412, are bonded together in a two-step process. If desired, a powder for inhibiting the formation of a harmful vapor phase which leads to rusting, may be dusted onto the tendons.

First, the joint is temporarily sealed by a light cement or grout. After this material hardens, a permanent joint is formed by pumping epoxy thereinto. Such two-step process is described in greater detail hereinafter.

FIGS. 610 show the constructional details of a bulkhead module 240, which, like frame modules 24a, 24b extends across the full transverse width of the vessel. The bulkhead module has a plurality of metal ducts 26 extending therethrough, and the ducts are rigidly tied into the reinforcing steel network within the module. The reinforcing steel network is indicated by dotted lines in FIGS. 67.

Three large substantially rectangular recesses 27, 29 and 31 with centrally located annular openings 27a, 29a and 310 are formed in each bulkhead module 24c. Cement plugs 33 with diagonally extending ducts 35 are cast to fit into recesses 27 29 and 31, as best shown in FIG. 9. FIGS. 7-10 also reveal that the bulkhead module 240 is haunched; phrased in another manner, the maximum longitudinal dimension of the module at its top and bottom surfaces is greater than the longitudinal dimension of plug 33. The plugs are secured in the recesses 27, 29 and 31 of the bulkhead module 240 by the two-step sealing process noted above and described in greater detail hereinafter and are posttensioned to the frame by passing tendons through ducts 35 and then taking up on same. Plugs 33 act more or less as flat domes to resist hydrostatic pressure in either direction in the event of an accident.

At predetermined longitudinal intervals, bulkhead modules 246 are secured to the assembled modules in the same two-step bonding process described above. The number and spacing of the bulkhead modules 240 is detennined by the structural requirements of the particular marine vessel under construction. As noted, all modules 24a, 24b and 240 extend transversely across the entire width of the vessel and divide same into three compartments or holds.

After all of the frame modules 24a, 24b and bulkhead modules 240 that comprise hull 14 are joined together into a cohesive unit, tendons 28 which pass therethrough are longitudinally prestressed. The method of prestressing the tendons, and thus compressing the concrete hull, is discussed in detail at a later point in the specification.

FIG. 11 shows the plurality of identical frame modules 24a, 24b, and bulkhead modules 240 joined together to form hull 14. A pair of spaced bulkheads 240 with plugs 33 secured thereto divide hull 14 into six cells; the outwardly opening ends of cells 30a, 30b, and 300 are visible in FIG. 11. Three cells of identical size and shape are formed at the opposite end of the hull. The space amidships between the pair of spaced bulkhead modules 24c is dead-space in accordance with accepted Coast Guard design standards and does not receive any load therein.

After all of the longitudinal modules and bulkheads are joined together. and the prestressing of tendons 28 has been achieved, the exterior surface of bull 14 is coated with several applications of a coal-tar epoxy so that any depressions formed by the joints between adjacent modules are smoothed-over and made flush with the remainder of the hull. The same coal-tar epoxy may also be applied to the surfaces of the individual frame and bulkhead modules before they are rotated by the turning shoe and the frame is suspended from the gantry as shown in FIG. 4. Hull 14, when viewed in FIG. 12, has a substantially unbroken, relatively smooth exterior surface. The exterior coating provides added protection against corrosion.

FIG. 12 shows an unfilled storage tank 22 being inserted into cell 30a from one open end of hull 14. Tank 22 is retained in fixed position by saddles 34 and 36 which are secured to carriages 38 and 40, respectively. The carriages are movable along tracks so that the tank and the saddles can be removed from the carriages and inserted into the hull. After the carriages 38, 40 are withdrawn from cell 30a, the tanks are secured in place by joining upper, semi-circular saddles to the lower semi-circular saddles. A similar procedure is used to insert and retain tanks 22 into cells 301) and 300. Tanks are then inserted and retained in the three cells opening outwardly at the opposite end of the hull. In all, six tanks 22 are introduced into the six cells formed in hull 14.

After tanks 22 have been secured in place, plugs 33, which have been positioned at spaced intervals on the floor of hull 14, are jacked into position to fit into the recesses and fill the openings 27a, 29a, and 31a in each bulkhead module 240. Plugs 33 have been match cast to fill such openings with a perfect fit, as shown in FIGS. 8-10. After the plugs are fitted into position, the joint defined between the periphery of the plug and the corresponding opening is sealed by injecting epoxy therebetween. Alternatively, the joint may be sealed by the two-step process described above utilized in joining adjacent modules 24a, 24b together.

After the epoxy in the joint has hardened, prestressing tendons (not shown) are inserted through ducts 35 in the plug and through corresponding ducts in bulkhead module 240 to securely tie the plugs to the hull. In the unlikely event that it is desired to remove one or more tanks 22, the plugs can be cut out, the tank removed and/or replaced, and a new plug 33 cast, positioned, and post-tensioned to the bulkhead module 240. The plugs act as a flat dome to resist hydrostatic pressure from either direction in the event of an accident.

After tanks 22 are seated in fixed position, and plugs 33 are secured to the bulkhead modules 24c, bow 12 and stem 16 are constructed and secured to opposite ends of hull 14. As indicated in FIG. 13, bow 12 is constructed from a plurality of prestressed longitudinal modules that are bonded together in much the same manner as hull 14. The tip 12a of bow 12, however, is cast in place and need not be prestressed. Stern 16 is also constructed from a plurality of prestressed longitudinal modules that are bonded together in much the same manner as hull 14. The tip 16a of stern 16 is cast in place and need not be prestressed. The bow and stem are joined to hull 14 by the two-step bonding process described in detail above. It will be appreciated that while longitudinal modules 24a, 24b and bulkhead modules, 24c of hull 14 are substantially rectangular in shape when viewed in front elevation, the bottom surfaces of bow l2 and stern 16 are tapered to facilitate the movement of the barge through the water; also, the upper surface of bow 12 is curved to accommodate the forward ends of tanks 18 seated upon the deck of the barge. By designing and fabricating the bow and stem as doubly curved sections, i.e., sections curved in two planes, the shell strength is sufficiently great as to resist heavy impact forces, such as slamming.

After the sections 12, 14 and 16 have been joined together as indicated in FIG. 13, six additional tanks 18 are secured to the deck by means of arcuate saddles 20. Exterior tanks 18 are aligned with interior tanks 22 so that the stability of the vessel is enhanced. After all 12 of the tanks and the associated piping and control equipment have been installed, the barge is then launched.

FIGS. l4A-l4B when placed in side-by-side relationship, show the manner in which each module of the hull 14 is maintained in compression by a network of longitudinally extending prestressing tendons 28 and laterally extending prestressing tendons 42. Prestressing tendons 28 appear as circles in FIGS. l4Al4B, spaced about the periphery of the module and along its interior upstanding support beams 44a, 44b which define the interior cells 30a, 30b, 300, etc. The circular saddles, which are bolted together to retain tanks 22 in fixed position within each cell, are visible in FIGS. 14A-14B.

The exact number and position of laterally extending prestressing cables 42 may vary widely in accordance with various design considerations. However, in the preferred embodiment of the barge of FIGS. 1-20, a particularly simple arrangement has been found most desirable. To illustrate, a first prestressing cable 420 extends transversely across that portion of module 24 that forms the deck of the barge. A second prestressing cable 42b extends from the upper right hand or starboard corner of module 24 down the right-hand outer wall, then across that portion of module 24, that forms the bottom of the vessel, and lastly continues upwardly through the left hand or port outer wall. A pair of vertically extending prestressing cables 42c, 42d maintain concrete support beam 44a in compression, while another pair of cables 42e, 42f maintain support beam 44b in compression.

FIGS. ISA-15B show the manner in which tendons 28 are prestressed to constantly maintain compressive forces upon the concrete sections of the barge. The longitudinal modules, and the ducts 26 passing therethrough, are omitted for the sake of clarity and only the bulkheads 24c are shown. To the extent possible, the tendons are maintained in a straight horizontal orientation for maximum effectiveness. The ends of the cables are anchored in the bulkheads, and the desired tensioning forces may be applied by hydraulic jacks, or other well-known techniques. After the tendons are tensioned, any excess length is trimmed, and then grout is pumped into the ducts and allowed to harden so that the tendons retain their horizontal orientation.

FIG. 16 shows the vertical orientation of exterior tanks 18 and exterior tanks 22. As noted previously, the particular alignment illustrated has proven to be the most stable arrangement for the preferred embodiment of the barge. While the saddles for the interior tanks are formed by two semi-circular halves bolted together, the lower portions of the saddles 20 may well comprise a unitary casting with a series of arcuate openings. Alternatively, the lower portions of saddles may comprise a metal support with a series of arcuate openings. A layer of insulating material is inserted between the tanks and the surrounding saddles to minimize heat transfer to the liquified gas and thus cause decreased boil-off and/or reduce the amount of refrigeration required.

FIGS. 17 and 18 illustrate, in detail, the two-stepprocess for bonding together the contiguous surfaces of the longitudinal modules, such as modules 24a and 24b and bulkhead modules 246. The sealing material, such as tape, that prevents material from accumulating in metal ducts 26 as each module is cast, is removed prior to rotating the module through a 90 are by the rotating shoe and suspending the module from a gantry. Neoprene O-rings or gaskets 44 are then glued in recesses 46 located at opposite longitudinal ends of the module. Alternatively, only one washer 44 may be used in one recess 46 at one end of the module. In both instances, the gasket fits against the face of the adjacent segment and seals duct 26 against the entry of epoxy during the injection thereof in the two-step bonding process.

The modules are brought into proximity with one another by lightly stressing longitudinally extending tendons 28 so that the modules can be effectively bonded together. The adjacent surfaces are then treated, as by bush hammering, wet sandblasting or jet sandblasting, to remove all laitance and expose the coarse aggregate. The joint is then sealed all the way around the perimeter of the modules to a depth of one inch, with a stiff mortar or a caulking compound. The grout may be introduced into the joint by conventional caulking guns 48. The approximately annular seal formed by the grout is indicated by reference numeral 50.

After the grout has hardened sufficiently to form a temporary joint, holes are then drilled or formed through grout 50 on 24 inch centers. The joint is then sealed all the way around the perimeter of the modules with an epoxy resin 52 that is injected by needle-nosed guns 54 through the holes. The pointed nose of gun 54 is inserted through the holes and then the epoxy resin 52 is injected into the annular space defined interiorly of the previously formed grout seal 50 until the epoxy comes out of the adjacent hole. Then gun 54 is moved to the next hole, and the process is repeated until the adjacent modules are firmly and permanently bonded together.

The sequence of operations involved in forming the permanent joint is illustrated in FIG. 17. The joint between a bulkhead module 240 and a module to the left thereof has only been formed to the extent that tendons 28 have been prestressed sufficiently to bring the adjacent modules close enough so that gaskets 44, 46 contact one another. The joint between longitudinal modules 24b and bulkhead module 24c has been formed to the extent that a temporary bond consisting of a l-inch deep layer of grout 50 has been deposited by caulking guns 48. The joint between longitudinal modules 24a and 24b has almost been completed, for the pointed nose of gun 54 has been inserted through grout seal 50 and is injecting the epoxy adhesive 52 into the annular space between gasket 46 and grout seal 50. FIG. 18, which is taken long line 13l3 and in the direction indicated, more completely shows the manner in which epoxy resin 52 is injected.

FIG. 19 is a detailed vertical cross-sectional view of a representative fragment of the bottom of hull 14. The perpendicular relationship between longitudinally extending prestressing tendons 28 and laterally extending prestressing tendons 42 is clearly shown. Additionally, conventional reinforcing rods 56 or welded wire mesh are utilized in conjunction with the prestressing tendons to form a network for supporting, and acurately aligning, the metal ducts through which the tendons are passed. The tendons may be formed of a single strand of steel, or preferably, of several strands.

FIG. 20 is a detailed vertical cross-sectional view of a representative fragment of a bulkhead module 240. Once again, the perpendicular relationship between longitudinal tendons 28 and laterally extending tendons 42 is depicted, and the relationship of the tendons to the network of reinforcing rods 56 is also shown.

FIGS. 21-23 illustrate an alternative embodiment of a barge identified generally by reference numeral 58, constructed in accordance with the principles of the instant invention. In contrast to the preferred embodiment of FIGS. 1-20 which is ideally suited for transporting liquid petroleum gas (LPG) in an unmanned barge having an overall length of 375 feet, a beam of 96 feet, and a depth of 35 feet, the alternative embodiment of FIGS. 2l-23 is ideally suited for transporting liquid natural gas (LNG). The dimensions for the LNG barge 58 are 675 feet in length, 86 feet across the beam, and 34 feet in depth. Barge 58 has a full load draft of 26 feet, as roughly approximated by FIGS. 22 and 23.

Barge 58 has three tanks 60 mounted on its deck by pairs of spaced saddles 62. A layer of insulating material 64 is positioned between the curved deck of the barge and the exterior of the tank, as seen in FIG. 23. A pair of spaced bulkheads 66 extend along substantially the entire length of barge 58 and impart structural rigidity to the vessel. The barge is fabricated in the same modular manner as barge 10.

FIGS. 24-27 depict various other marine vessels that are fabricated in the same manner as barges l0 and 58. FIG. 24 shows a floating platform 60 that has a plurality of storage tanks 62 secured therein. Tanks 62, which may contain LNG, LPG or similar fuels, supply fuel to power generating station 64 including a plurality of gas burning turbines; the fuel is burned to turn the turbines and thus produce electrical power which is transmitted over power lines 66 to remote locations. Platform 60 may thus serve as a self-contained power generating station, in case of a natural or man-made disaster, the platform may be towed to an off-shore site, be secured there by an anchor 68, and the electricity may be delivered directly to the affected locale.

FIG. 25 shows a floating platform 70 utilized as a selfcontained waste treatment facility, while FIG. 26 shows a floating platform 72 utilized as a cargo terminal. The ships can draw up alongside the platform to load and unload cargo, and a building 74 is situated atop the platform to store the cargo. FIG. 27 shows a floating platform 76 that serves as a heliport or as an emergency landing strip for small aircraft. Hangars 78, 80 are located at opposite ends of the landing strip. In all instances, gas for maintaining the operation of the floating platform is stored in tanks within the interior of the platform.

Manifestly, changes can be made in the sequence of steps involved in the fabrication technique without departing from the scope of the instant invention. To illustrate, the two-step bonding process of bonding the modules could be replaced by a process wherein epoxy could be placed on the matching faces and then the segments would be pulled together.

Similarly, changes in the structural configuration of the longitudinal modules and the bulkhead modules are equally feasible. For example, as shown in FIGS. 28 and 29 longitudinal module 24a may be formed with a depending rib 82 and an aligned, upstanding rib 84 at one face thereof. Such ribs extend transversely across the width of the module. When assembled in final position, the ribs are situated at closely spaced centers of approximately 4-6 feet, and substantially increase the ability of hull 14 to absorb hydrostatic forces.

FIG. 30 depicts another modification in the configuration of modules 24, wherein longitudinal ribs 86 are cast about the perimeter of the openings in the modules. Such longitudinal ribs enabled a thinner wall to be utilized for each module without sacrificing any of the structural rigidity of the thicker wall of the module. The thinner wall and ribs function as a T-beam to transmit hydrostatic forces to the transverse ribs, such as ribs 82 in FlGS. 28 and 29. The previously described step of vertically casting the modules makes the thin wall and rib configuration a practical reality.

it will be apparent that the marine vessels formed by the above described techniques are susceptible of assuming diverse forms and dimensions; for example, such vessels may be utilized as storage facilities in sheltered harbors or may be employed as pontoons for bridges or dry-docks. Hence, the claims should be liberally construed commensurate with the advance in the arts and sciences to which the invention appertains.

What is claimed is:

l. A method for fabricating prestressed concrete marine structures comprising the steps of:

a. forming upwardly opening molds whose dimensions correspond to the full transverse width and height dimensions of the marine structure being fabricated,

b. inserting a reinforcing steel network into each of the molds,

c. tieing a plurality of ducts into each one of said networks,

d. vertically casting a plurality of modules in an overlapping progression so that the joint defined between succeeding modules will match closely,

e. curing each of said modules,

f. rotating each of said modules into its normal vertical orientation,

g. applying prestressing to the reinforcing network within the cured modules in two planes that are normal to one another,

h. longitudinally passing steel tendons through the ducts in each of the modules after its rotation,

i. sequentially positioning each of said modules along the tendons in proximity to the adjacent module to define a matching joint therebetween,

j. bonding said modules together along the matching joints, and

k. strongly prestressing the steel tendons in a third plane that is normal to both of said planes to thus exert great compressive forces upon the modules that comprise the marine structure.

2. The method as defined in claim 1 further including the step of:

k. shaping the interior of certain of said upwardly opening molds so that each bulkhead module cast therein will be thickest at its top and bottom surfaces when viewed in side elevation and will taper inwardly to form a central section of reduced thickness.

3. The method as defined in claim 2 also including the steps of:

l. further shaping the interior of certain of said upwardly opening molds so that the central section of each bulkhead module cast therein has large openings extending therethrough,

m. casting concrete plugs to fit within said large openings,

n. inserting ducts into said plugs prior to casting same,

0. passing steel tendons through said ducts in said plugs after casting same, and

p. prestressing said plugs to the concrete bulkhead modules included within the marine structure.

4. The method as defined in claim 2 including the step of:

q. shaping the interior of certain others of said upwardly opening molds so that each longitudinal module cast therein will have a transversely extending rib defined at one face thereof, said rib subsequently aiding in accurately defining the joint between adjacent modules.

5. The method of claim 1 wherein the bonding step further includes the two steps of initially forming a temporary joint between adjacent modules and then forcing an adhesive through the temporary joint to form a permanent, water-tight bond between adjacent modules.

6. The method of claim 5 further including the steps of allowing the temporary joint to harden, drilling holes through the temporary joint on spaced centers, and introducing the adhesive into the space between the adjacent modules.

7. The method as defined in claim 6 wherein sufficient adhesive is introduced into each hole until some adhesive exits through the adjacent hole.

8. A prestressed concrete marine vessel comprising a. a bow, b. a stern, c. a prestressed concrete hull including:

1. a plurality of vertically oriented longitudinal modules,

2. a reinforcing steel network positioned within each of said modules for prestressing said modules in first and second directions, that are perpendicular to one another,

3. said longitudinal modules having a plurality of small openings extending longitudinally therethrough,

4. steel tendons passing longitudinally through said openings in each of said modules in a third direction perpendicular to the first and second directions,

5. a lesser plurality of bulkhead modules longitudinally interspersed within said plurality of longitudinal modules along bow, hull and stern,

6. each of said bulkhead modules having a plurality of spaced, centrally situated openings and a like plurality of plugs bonded to said bulkhead modules to seal said centrally situated openings,

7. bonding means securing adjacent modules together, and

8. anchoring means securing said tendons to said bulkhead modules so that prestressing forces applied to said tendons are transmitted to said vessel as compressive forces.

9. The vessel as defined in claim 8 wherein said plugs have ducts extending therethrough and steel tendons passing through said ducts and into said bulkhead modules for joining said plugs to said bulkhead modules.

10. The vessel as defined in claim 9 wherein the ducts pass diagonally through said plugs and said bulkhead modules.

11. The vessel as defined in claim 8 wherein the maximum longitudinal dimensions of the bulkhead modules occurs at its top and bottom surfaces, and said bulkhead modules taper inwardly to a central section of reduced thickness, the longitudinal dimension of said plugs being substantially equal to the longitudinal dimension of the central section.

12. A bulkhead module adapted to be utilized in a concrete marine structure, said bulkhead module comprising:

a. a concrete body having a transverse dimension equal to the width of said marine structure,

b. a reinforcing steel network positioned within said concrete body,

c. said concrete body being thickest at its top and bottom surfaces when viewed in side elevation and tapering inwardly to form a central section of reduced thickness,

d. said central section having large openings extending longitudinally therethrough, and

e. concrete plugs secured within said openings to close said large openings in said bulkhead.

13. The bulkhead module as defined in claim 12 wherein said plugs have ducts extending therethrough and said concrete body has ducts aligned with the ducts in said plugs, and steel tendons are passed through said aligned ducts to prestress said plugs to said concrete body.

14. The bulkhead module as defined in claim 12 wherein said central section of the concrete body has substantially rectangular recessed portions formed therein, the openings being circular in shape and being located in the middle of the recessed portions, and plugs being slightly smaller in size than said recessed portions.

15. The bulkhead module as defined in claim 12 wherein longitudinally extending ribs are spaced about the walls defining said openings.

16. A longitudinal frame module adapted to be utilized in a concrete marine structure, said module comprising a. a concrete body having a transverse dimension equal to the width of the marine structure and a height dimension equal to the height of the marine structure,

b. said concrete body having an integrally formed pair of spaced side walls, a bottom slab and a deck slab spaced parallel thereto, said walls and slabs defining an open rectangular chamber,

c. support beams extending vertically between said bottom slab and said deck slab, and parallel to said side walls, to divide said chamber into a plurality of cells,

d. a reinforcing steel network positioned within said body for prestressing said body in first and second complimentary directions, and e. a rib formed at one face of the body and extending transversely across the width of the frame module.

17. A marine structure fabricated of prestressed concrete comprising:

a. a plurality of integrally cast longitudinal modules,

each of said longitudinal modules comprising:

1. a concrete body having a transverse dimension equal to the width of the marine structure and a height dimension equal to the height of the marine structure,

2. said concrete body having an integrally cast pair of spaced side walls, a bottom slab and a deck slab spaced parallel thereto, said walls and slabs defining an open rectangular chamber,

3. support beams extending vertically between said bottom slab and said deck slab, and parallel to said side walls, to divide said chamber into a plurality of cells,

4. said walls, slabs and support beams having a plurality of openings extending longitudinally therethrough,

5. a reinforcing steel network positioned within said body for prestressing said body in first and second directions, that are perpendicular to each other,

b. a lesser plurality of integrally cast bulkhead modules, each of said bulkhead modules comprising: 1. a concrete body having a transverse dimension equal to the width of the marine structure and a height dimension equal to the height of the marine structure,

2. a reinforcing steel network positioned within said concrete body for prestressing said body in first and second directions, that are perpendicular to each other,

3. said concrete body being thickest at its top and bottom surfaces when viewed in side elevation and tapering inwardly to form a central section of reduced thickness,

4. said central section having large openings extending longitudinally therethrough, and

5. concrete plugs secured within said openings to close said openings in said bulkhead module,

6. said concrete body having a plurality of smaller openings extending longitudinally therethrough,

c. means for bonding said modules together with said lesser plurality of bulkhead modules interspersed within said longitudinal modules, and

d. a plurality of steel tendons anchored at the interspersed bulkhead modules and passing through said longitudinal modules,

e. said tendons being prestressed in a third direction perpendicular to said first and second directions and corresponding to the longitudinal extent of the structure to thereby continuously exert great compressive forces upon all of said modules to form a cohesive structural unit. 

1. A method for fabricating prestressed concrete marine structures comprising the steps of: a. forming upwardly opening molds whose dimensions correspond to the full transverse width and height dimensions of the marine structure being fabricated, b. inserting a reinforcing steel network into each of the molds, c. tieing a plurality of ducts into each one of said networks, d. vertically casting a plurality of modules in an overlapping progression so that the joint defined between succeeding modules will match closely, e. curing each of said modules, f. rotating each of said modules into its normal vertical orientation, g. applying prestressing to the reinforcing network within the cured modules in two planes that are normal to one another, h. longitudinally passing steel tendons through the ducts in each of the modules after its rotation, i. sequentially positioning each of said modules along the tendons in proximity to the adjacent module to define a matching joint therebetween, j. bonding said modules together along the matching joints, and k. stronGly prestressing the steel tendons in a third plane that is normal to both of said planes to thus exert great compressive forces upon the modules that comprise the marine structure.
 2. The method as defined in claim 1 further including the step of: k. shaping the interior of certain of said upwardly opening molds so that each bulkhead module cast therein will be thickest at its top and bottom surfaces when viewed in side elevation and will taper inwardly to form a central section of reduced thickness.
 2. a reinforcing steel network positioned within each of said modules for prestressing said modules in first and second directions, that are perpendicular to one another,
 2. said concrete body having an integrally cast pair of spaced side walls, a bottom slab and a deck slab spaced parallel thereto, said walls and slabs defining an open rectangular chamber,
 2. a reinforcing steel network positioned within said concrete body for prestressing said body in first and second directions, that are perpendicular to each other,
 3. said concrete body being thickest at its top and bottom surfaces when viewed in side elevation and tapering inwardly to form a central section of reduced thickness,
 3. support beams extending vertically between said bottom slab and said deck slab, and parallel to said side walls, to divide said chamber into a plurality of cells,
 3. said longitudinal modules having a plurality of small openings extending longitudinally therethrough,
 3. The method as defined in claim 2 also including the steps of: l. further shaping the interior of certain of said upwardly opening molds so that the central section of each bulkhead module cast therein has large openings extending therethrough, m. casting concrete plugs to fit within said large openings, n. inserting ducts into said plugs prior to casting same, o. passing steel tendons through said ducts in said plugs after casting same, and p. prestressing said plugs to the concrete bulkhead modules included within the marine structure.
 4. The method as defined in claim 2 including the step of: q. shaping the interior of certain others of said upwardly opening molds so that each longitudinal module cast therein will have a transversely extending rib defined at one face thereof, said rib subsequently aiding in accurately defining the joint between adjacent modules.
 4. steel tendons passing longitudinally through said openings in each of said modules in a third direction perpendicular to the first and second directions,
 4. said walls, slabs and support beams having a plurality of openings extending longitudinally therethrough,
 4. said central section having large openings extending longitudinally therethRough, and
 5. concrete plugs secured within said openings to close said openings in said bulkhead module,
 5. a reinforcing steel network positioned within said body for prestressing said body in first and second directions, that are perpendicular to each other, b. a lesser plurality of integrally cast bulkhead modules, each of said bulkhead modules comprising:
 5. a lesser plurality of bulkhead modules longitudinally interspersed within said plurality of longitudinal modules along bow, hull and stern,
 5. The method of claim 1 wherein the bonding step further includes the two steps of initially forming a temporary joint between adjacent modules and then forcing an adhesive through the temporary joint to form a permanent, water-tight bond between adjacent modules.
 6. The method of claim 5 further including the steps of allowing the temporary joint to harden, drilling holes through the temporary joint on spaced centers, and introducing the adhesive into the space between the adjacent modules.
 6. each of said bulkhead modules having a plurality of spaced, centrally situated openings and a like plurality of plugs bonded to said bulkhead modules to seal said centrally situated openings,
 6. said concrete body having a plurality of smaller openings extending longitudinally therethrough, c. means for bonding said modules together with said lesser plurality of bulkhead modules interspersed within said longitudinal modules, and d. a plurality of steel tendons anchored at the interspersed bulkhead modules and passing through said longitudinal modules, e. said tendons being prestressed in a third direction perpendicular to said first and second directions and corresponding to the longitudinal extent of the structure to thereby continuously exert great compressive forces upon all of said modules to form a cohesive structural unit.
 7. bonding means securing adjacent modules together, and
 7. The method as defined in claim 6 wherein sufficient adhesive is introduced into each hole until some adhesive exits through the adjacent hole.
 8. anchoring means securing said tendons to said bulkhead modules so that prestressing forces applied to said tendons are transmitted to said vessel as compressive forces.
 8. A prestressed concrete marine vessel comprising a. a bow, b. a stern, c. a prestressed concrete hull including:
 9. The vessel as defined in claim 8 wherein said plugs have ducts extending therethrough and steel tendons passing through said ducts and into said bulkhead modules for joining said plugs to said bulkhead modules.
 10. The vessel as defined in claim 9 wherein the ducts pass diagonally through said plugs and said bulkhead modules.
 11. The vessel as defined in claim 8 wherein the maximum longitudinal dimensions of the bulkhead modules occurs at its top and bottom surfaces, and said bulkhead modules taper inwardly to a central section of reduced thickness, the longitudinal dimension of said plugs being substantially equal to the longitudinal dimension of the centRal section.
 12. A bulkhead module adapted to be utilized in a concrete marine structure, said bulkhead module comprising: a. a concrete body having a transverse dimension equal to the width of said marine structure, b. a reinforcing steel network positioned within said concrete body, c. said concrete body being thickest at its top and bottom surfaces when viewed in side elevation and tapering inwardly to form a central section of reduced thickness, d. said central section having large openings extending longitudinally therethrough, and e. concrete plugs secured within said openings to close said large openings in said bulkhead.
 13. The bulkhead module as defined in claim 12 wherein said plugs have ducts extending therethrough and said concrete body has ducts aligned with the ducts in said plugs, and steel tendons are passed through said aligned ducts to prestress said plugs to said concrete body.
 14. The bulkhead module as defined in claim 12 wherein said central section of the concrete body has substantially rectangular recessed portions formed therein, the openings being circular in shape and being located in the middle of the recessed portions, and plugs being slightly smaller in size than said recessed portions.
 15. The bulkhead module as defined in claim 12 wherein longitudinally extending ribs are spaced about the walls defining said openings.
 16. A longitudinal frame module adapted to be utilized in a concrete marine structure, said module comprising a. a concrete body having a transverse dimension equal to the width of the marine structure and a height dimension equal to the height of the marine structure, b. said concrete body having an integrally formed pair of spaced side walls, a bottom slab and a deck slab spaced parallel thereto, said walls and slabs defining an open rectangular chamber, c. support beams extending vertically between said bottom slab and said deck slab, and parallel to said side walls, to divide said chamber into a plurality of cells, d. a reinforcing steel network positioned within said body for prestressing said body in first and second complimentary directions, and e. a rib formed at one face of the body and extending transversely across the width of the frame module.
 17. A marine structure fabricated of prestressed concrete comprising: a. a plurality of integrally cast longitudinal modules, each of said longitudinal modules comprising: 